1. Field of the Invention
This invention relates to power trowels, and more particularly, to engine driven power trowels having lever-actuated blade pitch adjustment mechanisms.
2. Description of the Prior Art
Various types of engine driven power trowels are currently available in the marketplace. Such trowels typically include a frame, an internal combustion engine coupled to the frame and three or four horizontally oriented, symmetrically disposed trowel blades. An upwardly extending trowel handle having a pair of handlebar grips enables an operator to control the movement of the trowel to complete finishing operations on partially cured concrete. Various blade pitch control mechanisms have been provided on such power trowel units to enable an operator to adjust the trowel blade pitch before or during finishing operations.
Superior Featherweight Tool Company of City of Industry, Calif., manufactures a Model GH power trowel which includes a lever-actuated blade pitch control unit. The lever arm adjustment mechanism is pivotally coupled to the trowel frame at a position close to the central axis of the trowel blades. Downward displacement of the outboard end of the lever arm results in upward displacement of the inboard end of the lever arm which is coupled to a swash plate. The resulting upward swash plate movement increases the blade pitch angle. This direct coupled, lever-actuated blade pitch adjustment mechanism permits an operator to rapidly change the pitch of the rotating trowel blades.
Another commercially available engine driven trowel of the type illustrated in FIGS. 1 and 2 provides a rotatable blade pitch adjustment wheel located between the handlebar grips of the trowel handle. Rotation of this handle in a clockwise or counterclockwise direction either gradually increases or gradually decreases the blade pitch. Rotation of that wheel actuates a threaded adjustment mechanism which is coupled within the trowel handle to a steel cable. The remote end of the steel cable is coupled to a swash plate actuator arm. To increase the blade pitch angle, the blade pitch adjustment wheel is rotated to actuate the threaded adjustment mechanism to retract the steel cable further into the trowel handle to thereby upwardly displace the outboard end of the swash plate actuator arm and downwardly displace the inboard end of the actuator arm. Swash plate displacements of this prior art power trowel produce blade pitch changes just the reverse of those produced by the Superior Featherweight power trowel discussed above, where an upward displacement of the swash plate increases blade pitch.
Certain power trowel users prefer the rapidly adjustable lever arm linkage of the type incorporated on the Superior Featherweight power trowel, while other users prefer the slower but more precisely adjustable blade adjustment mechanism of the type incorporated in the trowel depicted in FIGS. 1 and 2.